Field of the Invention:
This invention relates to the field of methods and chemicals for the treatment of nematodes in soil, and particularly to a method using bromonitromethane which proves to be highly efficacious as a nematicide at low levels.
Description of the Prior Art:
Nematodes are slender, worm-like organisms found in the soil almost anywhere in the world. Most nematodes range from one-fiftieth to one-twenty-fifth inches long. Nematodes reproduce by eggs and typically progress through four larval stages to adulthood.
Some nematodes are plant parasitic, and more than one thousand species of nematodes are known to be harmful to plants. Many plants are affected by nematodes, including soybeans, peanuts, cotton, tobacco, strawberries, root crop, ornamentals, citrus, vegetables and many other crops. Nematodes feed on the roots and lower stems of plants, and some attack the leaves and flowers. Some species of nematodes inadvertently introduce pathogenic, root-invading microorganisms into the plants while feeding. Nematodes may also predispose plant varieties to other disease causing agents, such as wilts and root rots. In other instances, the nematodes themselves cause the disease, disrupting the flow of water and nutrients in the xylem system, resulting in root-knot or deprivation of the above-ground parts, and ultimately causing stunting. Symptoms of nematode infestation include swellings, thickenings, galls and distortions of above-ground components of the plant, and root conditions such as short stubby roots, lesions (dead spots), swellings, galls and general breakdown. See, "The Mutagenicity of Pesticides" by Samuel S. Epstein and Marvin S. Legator, MIT Press, 1971.
The extent of crop loss to nematode infestation is substantial and widespread. Yield losses in agricultural crops in the United States and throughout the world are enormous, and have been labelled as "appalling" by experts in the field. For example, the losses due to nematode infestation for New Jersey alone were estimated as fifteen million dollars in one year, and losses for the entire United States may be as much as five hundred million dollars per year. See, "Handbook on Biological Control of Plant Pests" by Waldimero Coscarelli, Plants & Gardens publication, Vol. 16, No.3, 1960.
There has been a substantial need for chemical controls to limit the damage caused by nematodes and to curb their spread to unifested fields. Nematicides have been available in the prior art, some of which were useful as fumigants. The most effective and widely used control agents have been methyl bromide and EDB (ethylene dibromide), and certain chlorinated compounds including D-D (1,3-dichloropropene,1,2-dichloropropane), DBCP (1,2-dibromo-3 -chloropropane), and Telone (1,3-dichloropropene). In U.S. Pat. No. 3,445,576, issused to Kenaga on May 20, 1969, there is disclosed the use of bromodifluoronitromethane for controlling nematodes, insects and fungi. Other nematicides generally fall within three groups: (1) organophosphate insecticides, (2) isothiocyanates, and (3) carbamate or oxime insecticides. For example, Vapam (sodium N-methyl dithiocarbamate) has proven to be useful, especially as a pre-plant treatment.
Some of the better known nematicides have been in use for many years. The nematicidal properties of DD and EDB, for example, were discovered in 1943 and 1945 and effectively launched the use of volatile nematicides on a field-scale basis. Previously only seedbeds, greenhouse beds, and potting soil had been treated, with materials such as chloropicrin (trichloronitromethane), carbon disulfide and formaldehyde. These were very expensive, in some instances explosive, and usually required a surface seal because of their relatively high vapor pressures. See, "The Pesticide Book" by George W. Ware, W. H. Freeman & Co., 1978.
Many of the time-tested nematicides, however, have fallen by the wayside because of carcinogenicity, toxicity and environmental problems. DBCP, for example, was found to be relatively cheap and effective, but has been cancelled as a carcinogen. Methyl bromide is lethal to all plant and animal life, and is classified as a sterilant which should be used at least two weeks before planting to avoid its total phytotoxic effect. Attempts to substitute non-fumigants, dithiocarbamates and methyl isothiocyanates have been mostly unsuccessful because of the expense and the limited efficacy of those materials.
Reference to other chemical pesticides has not proven to be very helpful. There are numerous forms of pesticides adapted to the treatment of particular pests. These include, for example, insecticides, herbicides, fungicudes, rodenticides, bactericides, acaricides, algicides, miticides, molluscicides, avicides, slimicides, piscicides and ovicides, as well as disinfectants, growth regulators, defoliants, desiccants, repellents, attractants and chemosterilants. The operation of the different types of pesticides varies according to the pests being treated. For example, the known or suspected major modes of chemicals for treating plants (including herbicides, fungicides, etc.) include: (a) inhibition of photosynthesis, (b) inhibition of oxidative phosphorylation, (c) hormone analogs, (d) inhibition of pantothenate synthesis and (e) inhibition of porphyrin, hence of chlorophyll synthesis. In contrast, the operation of chemicals for the treatment of animals (insecticides, nematicides, etc.) include: (a) inhibition of acetylcholinesterase, (b) inhibitions of neuromuscular junction and (c) neurotoxication. There have consequently been a vast number of known pesticides covering a large variety of chemicals operating in differing fashions. However, few effective nematicides have been discovered in the prior art.
There has therefore remained a longstanding and substantial need for a nematicide which is effective, and does not have the disadvantages of the prior art chemicals. The elimination of cheap, effective fumigant nematicides and the poor performance of remaining controls are forcing some crops out of production in the traditional nematode-infested areas of the United States. Also, some nematodes are beginning to spread to new areas never before troubled by these pests, as evidenced by the appearance of the soybean cyst nematode in the midwestern United States. While the need continues to grow, concerns over the inherent toxicity of contact nematicides, and environmental problems from high rates of application (such as leaching into ground water) will undoubtedly result in the restriction or elimination of some or all of the remaining know products.
The present invention is based upon the discovery that bromonitromethane is highly effective as a nematicide, particularly as a fumigant, and does not have the high expense or toxicity associated with certain prior art compounds. Heretofore, bromonitromethane was long ago indicated to be useful only as a fungicide, as disclosed in U.S. Pat. No. 2,763,962, issued to Hardy on Sept. 25, 1956. However, it is believed that this chemical was never given governmental approval or used commercially, and that no other uses for the chemical have been described until now.